The present invention relates to a lamp having a shading film and a method for manufacturing the same. More particularly, the present invention relates to a lamp in which a greensheet as a shading film is applied and fired for integration and a method for manufacturing the same.
Conventionally, a shading film is formed on a discharge lamp, a tungsten halogen lamp or the like. An example of a discharge lamp will be described below. A discharge lamp having a wattage as low as a lamp power of 35 W is put to practical use. Since the discharge lamp is small and has a high efficiency, it is used for an automobile headlight, a light source for the back light of a liquid crystal projector, or the like.
When the discharge lamp is used for an automobile headlight or a light source for the back light of a liquid crystal projector, the discharge lamp is combined with a reflecting mirror. In recent years, a discharge lamp using quartz, which cuts off ultraviolet rays, for an outer tube to prevent the reflecting mirror from deteriorating due to ultraviolet rays emitted from the discharge lamp is known. In general, in order to achieve a proper light distribution by combining the reflecting mirror and the discharge lamp, the position of the light-emitting portion, that is, the arc, should be controlled with a very high precision with respect to the reflecting mirror. However, since the arc, which is the light-emitting portion of the discharge lamp, is affected by such factors as the shape of the arc tube, pressure, tube voltage, and tube current, it is difficult to control the position of the light-emitting portion mechanically in the same manner as the filament of a bulb or the like.
Accordingly, a method for obtaining a precise light distribution by forming a shading film on the outer tube and optically cutting a part of the arc whose position is difficult to control is proposed. With this method, the light distribution depends on the accuracy of the position of the shading film rather than the arc. Therefore, it is necessary to coat the outer tube with the shading film with a good positional accuracy.
Conventional lamps have an arc tube surrounded by an outer tube. An outer lead extends from each electrode to each contact of a base to which the neck-shaped portion of the arc tube is fixed. The power supply line of one outer lead extends along the outer surface of the outer tube. The outer tube is coated with a shading film near its neck-shaped portion and on the side distant from the power supply line by using a brush or an ink jet. Also, the outer tube is coated with a belt-shaped shading film at both ends of the discharge path between the electrodes and on the side facing the power supply line (Japanese Patent Application No. (Tokuhyo Hei) 9-500489).
However, with such a method for forming a shading film by using a brush or an ink jet, coating with a shading film must be performed by a machine. Therefore, the machine cost and the coating time are necessary. In addition, the control of a coating material for the shading film and the coating step are complicated.
Furthermore, with the above method, variations in the thickness of the shading film occur easily during coating. Also, since the coating material is a liquid, the thickness of the border portion of the formed shading film is smaller than that of the central portion of the shading film. Therefore, the shading property of the border portion of the shading film and its vicinity after firing deteriorates. That is, there is a problem that the edge of the border portion of the shading film has a gentle slope structure. In the lamp that controls the light distribution by the shading film, the positional accuracy and linearity of the border portion of the shading film coated on the outer tube affect the light distribution significantly. Therefore, it is necessary to control the shading film, especially the border portion of the shading film, with a good positional accuracy.
In order to solve the conventional problems as described above, it is an object of the present invention to provide a lamp that provides a more precise light distribution property by making the border portion of the shading film steep, making the positional accuracy good, and ensuring the thickness uniformity of the shading film. It is another object of the present invention to provide a method for manufacturing such a lamp simply at a low cost.
In order to achieve the above objects, the present invention provides a lamp comprising a glass substrate and a shading film formed on a surface of the glass substrate, wherein the shading film is integrated with the surface of the glass substrate by applying a greensheet comprising an inorganic pigment and an inorganic matrix component to the surface of the glass substrate and firing the greensheet. Here, the greensheet means a precursor sheet that comprises an inorganic substance, such as ceramic or glass, as a matrix component and is used to obtain a sintered body. The greensheet is flexible and can be used by itself. Therefore, it is easy to prepare a greensheet having a uniform thickness ahead of time. Also, it is easy to pattern the greensheet into a predetermined shape previously by punching. In addition, since the greensheet has a smaller amount of an organic substance component than a coating material, the density of the sintered body is higher than in the case of baking the coating material. Furthermore, only a minor deformation occurs during sintering. Therefore, it is possible to make the border portion of the shading film steep, make the positional accuracy good, and ensure the thickness uniformity of the shading film. Thus, it is possible to make the light distribution property during lighting good. Furthermore, since the shading film of the present invention is formed by applying and firing a greensheet, the degree of freedom for a position where the shading film is formed improves, unlike the conventional shading film formed by using a brush or an ink jet. Therefore, the shading film can be formed in an optimum position, considering the light distribution property and the convenience of the manufacturing method. Thus, the light distribution property can be improved, and the lamp can be manufactured easily at a low cost.
It is preferable that the greensheet is patterned into a predetermined shape before being applied to the glass substrate, because a highly uniform shading film can be formed.
It is preferable that an edge of the shading film is steep. This makes the border portion (the end face) of the shading film more distinct, so that the light contrast can be clear at the edges of the shading film.
It is preferable that the inorganic pigment is at least one metal selected from the group consisting of iron, manganese, copper, chromium and cobalt, or a metal oxide thereof, because a shading film having a high shading property can be formed.
As the inorganic matrix component, a powder or fine particles of glass, earthenware, ceramics or the like can be used. The glass frit is preferable in view of the easiness of a heat treatment, because the glass frit is melted by heating to be easily integrated with the surface of the glass substrate. Here, the glass frit means glass or a powder or fine particles of the component of the glass.
The present invention provides a lamp comprising a shading film, wherein the shading film has a portion whose thickness is 90% or more of the maximum thickness of the shading film within the range of 0.5 mm from an edge of the shading film. According to this aspect, a shading film that has a distinct border portion (end face) and has only a minor nonuniformity in thickness can be formed with a good positional accuracy. This can make the light distribution property during lighting good.
It is preferable that the thickness of the shading film in the range of 0.5 mm and more inside from an edge of the shading film is 50% or more of the maximum thickness of the shading film, because a preferable shading property can be obtained.
It is preferable that the average thickness of the shading film in the range of 0.5 mm and more inside from an edge of the shading film is 10 to 100 xcexcm, because a preferable shading property can be obtained.
It is preferable that the light transmittance in the range of 0.5 mm and more inside from an edge of the shading film is 6% or less of the light transmittance of a portion of the glass substrate without the shading film, because the shading property is excellent in this range.
The shading film can be provided on a surface of the arc tube of the lamp. More specifically, the shading film can be provided on at least one of the outer and inner surfaces of the arc tube.
The shading film can be provided on a surface of an outer tube covering the arc tube of the lamp. More specifically, the shading film can be provided on at least one of the outer and inner surfaces of the outer tube.
It is preferable that the lamp is a discharge lamp. In the discharge lamp, the control of the arc position is especially difficult. By applying the present invention, a more precise light distribution property can be obtained, and the effect of the present invention can be provided significantly.
The present invention provides a method for manufacturing a lamp including a glass substrate and a shading film formed on a surface of the glass substrate, comprising applying a greensheet that comprises an inorganic pigment and an inorganic matrix component and is patterned into a predetermined shape to a surface of a glass substrate, and firing the greensheet so that the greensheet is integrated with the surface of the glass substrate, thereby forming a shading film. According to this method, the lamp of the present invention can be manufactured efficiently with a few manufacturing steps.
It is preferable that the inorganic matrix component is a glass frit, because the glass frit is melted by heating to be easily integrated with the surface of the glass substrate.
It is preferable that the firing comprises calcination and main firing.
It is preferable that the calcination is performed in a temperature range for removing the organic component in the greensheet.
It is preferable that the calcination is performed in an oxidative atmosphere at a temperature of 200 to 600xc2x0 C. According to the preferable example, the organic component in the greensheet can be removed efficiently.
It is preferable that the main firing is performed in an oxidative atmosphere at a temperature of 600 to 1,500xc2x0 C. According to the preferable example, the greensheet can be baked onto the glass substrate for integration.
It is preferable that at least one surface of the greensheet is coated with an adhesive, because the greensheet can be applied to the glass substrate easily. Thus, the number of manufacturing steps is reduced. Therefore, a lamp having a good light distribution property can be manufactured at a low cost. In addition, the adhesive does not affect the light distribution property and the like because the adhesive is lost during firing.
It is preferable that the average thickness of the greensheet is in the range of 10 to 100 xcexcm. According to the preferable example, a shading film having a preferable thickness can be obtained finally, so that a preferable shading property can be obtained.
Furthermore, by applying the above method to the manufacture of a discharge lamp, a more precise light distribution property can be achieved in a discharge lamp, whose arc position is difficult to control, with a few manufacturing steps and at a low cost. Therefore, the effect of the present invention can be provided significantly.